The reflectometer is used to determine the scattering
density profile as a function of depth from an air-material
interface or even at buried interfaces. This is especially useful
for characterizing magnetic multilayers used for recording
heads, polymer diffusion at interfaces and similar problems.
Although data collection is not rapid with this instrument, the
dynamic range is quite good, allowing for detailed determination
of the interfacial region. Typical measurements are carried out
by scattering neutrons in the grazing incidence geometry, beyond
the critical angle for total external reflection, as a function
of wave vector transfer Q (2sinq /
l), perpendicular to the reflecting
surface. This profile of reflectivity then can be related to
the neutron scattering length density (Nbc )
at depths of up to several thousand Å, with an effective
length resolution of a few Å. The samples must have a smooth,
flat surface, the individual layers must be smooth and have uniform
thickness throughout, and preferably several cm2 in area. The
method is extensively used for studies of polymer films and interfaces,
and thin films and multilayers of metals and superconductors,
both magnetic and non-magnetic.
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University of Missouri-Columbia
